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LM139: Input Voltage Range

Kiran Kerai
Intellectual 380 points

Part Number: LM139
Other Parts Discussed in Thread: LM397

LM139

The datasheet for this part states that the input common mode voltage can range from 0 V to VCC– 2 V. It also describes the outcomes of input voltage ranges that exceed this common mode range as follows:

• When IN– is higher than common mode and IN+ is within common mode, the output is low and the output transistor is sinking current

• When IN+ is higher than common mode and IN– is within common mode, the output is high impedance and the output transistor is not conducting

• When IN– and IN+ are both higher than common mode, the output is low and the output transistor is sinking current


Please confirm:

• whether this is guaranteed (or typical) operation of the device.

• my interpretation of the datasheet is that the device input voltage can exceed the supply rails. Is this correct? If so, please confirm what feature of this device makes in unique from other comparators that limit the input voltage to the supply rail.

• exceeding the common mode range of the device will not cause damage as long as the input voltage is within absolute maximum rating of -0.3 to 36V (stated in datasheet). If this is not the limit, please state the maximum input voltage that this device can withstand without damage.


 • What is the maximum voltage rating for transient voltage <200us? Particularly, I am interested in the lower limit of –0.3V. Can this device withstand –1V for duration <200us without damage?

 

• please confirm that allowable input voltage range when the LM139 is supplied with +/-12V rails.
 

• do your responses above apply to device LM397?

  • 0
    TI__Genius 17125 points
    Hello Kiran,

    TI makes many different versions and grades of the LM139, which have come from different sources. Can you tell us the exact part number you are interesed in.
    Also, what is the part number of interest for the LM397.
  • 0 in reply to Kirby Kruckmeyer96848
    Intellectual 380 points

    The LM139AD and LM397M.

    Please take into consideration that the comparator is supplied with +12V and 0V rails when responding to my queries.

     

    In addition, please confirm that allowable input voltage range when the LM139 is supplied with +/-12V rails.


    Many Thanks

  • 0 in reply to Kiran Kerai
    TI__Genius 17125 points
    Hello Kiran,
    This is the commercial version of the part that originated in TI and is covered by the LM139 product folder and LMx93x, LM2901xx datasheet.
    I am moving your question to the group that would support this.
  • 0
    TI__Guru 66646 points
    Hello Kiran,

    Confirming:

    • whether this is guaranteed (or typical) operation of the device.

    PG> We do not guarantee operation outside specified parameters. Because operation as stated above is outside table specs, it is not guaranteed, but it is generally expected due to the design.

    • my interpretation of the datasheet is that the device input voltage can exceed the supply rails. Is this correct? If so, please confirm what feature of this device makes in unique from other comparators that limit the input voltage to the supply rail.

    PG> The LMx39/x93 family is on an older process that has higher PNP breakdown voltages that prevent stress to the input devices and is better tolerated.

    When this device was designed in the early 1970's, ESD protection was not a big issue, so there are no dedicated ESD protection devices (diodes) added that would clamp the inputs to the supply pins. Therefore, the inputs may be taken above the supply rails without damage. But do NOT go below ground!

    However, when operating outside the common mode range as above, many specifications will change (prop delay, Vos, input bias current, etc) so specified limits are no longer valid.

    • exceeding the common mode range of the device will not cause damage as long as the input voltage is within absolute maximum rating of -0.3 to 36V (stated in datasheet). If this is not the limit, please state the maximum input voltage that this device can withstand without damage.

    PG> Correct. The inputs can withstand up to Abs Max (36V) *without damage*, regardless of supply voltage. However, this does not mean it will operate within the specifications if the table specs are violated.

    • What is the maximum voltage rating for transient voltage <200us? Particularly, I am interested in the lower limit of –0.3V. Can this device withstand –1V for duration <200us without damage?

    PG> As stated above, this device does not have any ESD protection, thus it does not have a defined path for reverse input voltages. The reverse voltage will find it's way through the paths of least resistance through the device substrate junctions. Many of these junctions are not designed to handle current and may cause "adverse effects".

    After -800mV, these junctions will be in full conduction and damage may be occurring. Long term reliability will be in doubt.

    "Damage" is a function of energy. But since what structure is getting this "energy" is unknown, a firm time or current limit cannot be established. Time as short as 1ns can cause irreversible damage if it his the wrong place. Continuous "hammering" of the junctions will degrade them over time and will shorten the device lifetime or cause parameters to drift long-term.

    If negative voltages are expected, they should be limited to less than 1mA (or less) with series resistance. An external Schottky clamp diode is recommended if reverse voltages will be frequent as this diode will clamp earlier and take the brunt of the current.

    • please confirm that allowable input voltage range when the LM139 is supplied with +/-12V rails.

    +10V to -12.3V

    • do your responses above apply to device LM397?

    PG> Yes. The LM397 is a newer device built on a newer process, but using the same basic circuit topology to mimic the LMx39. It does contain a "snapback" ESD diode which still allows the input to go above V+, but it will clamp when the voltage is too high (actual voltage not specified - but >40V).